Simulium larvae perform two behaviors in response to physical contact with invertebrate predators: curling and drifting. Curling involves the attachment of a silk thread to the substrate (in preparation for drifting), and drifting allows an individual to quickly leave the vicinity of the predator. The purpose of this study is to determine if larval black flies (Simulium vittatum s. s.) from two field sites respond to chemical stimuli from damaged conspecifics in a manner consistent with responses to predator contact. In experiment 1, we observed the responses of individual S. vittatum to chemicals from damaged members of their own population (Houghton Creek or Sixtown Creek). In experiment 2, we examined larval responses to chemicals from damaged individuals from both sites in order to determine if larvae adjusted their responses based on the source of the stimulus. The results of experiment 1 show that larvae from each population are significantly more likely to engage ‘curling’ when exposed to damaged conspecifics versus a control. In addition, the duration of the curling behavior was significantly longer when exposed to chemicals from damaged conspecifics compared to a control. The results of experiment 2 demonstrate that individual larvae are more likely to curl when exposed to damaged conspecifics as compared to a control, regardless of the source population of the stimulus donors. We again found that the duration of the curling behavior was significantly longer when exposed to the damaged conspecifics versus the control with no significant difference in the responses to the different source populations. These results offer preliminary evidence to suggest that larval S. vittatum are able to detect and respond to chemicals associated with predation in a natural setting and that there does not appear to be population differences with regard to the nature of the response or the stimulus.
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Vol. 166 • No. 1